Non-reciprocal ferrite switch with alternate conductive and resistive plates



l5 r1l 6, 1965 AKIRA cHo ETAL 3,

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVEPLATES Filed Oct. 26. 1961 4 Sheets-Sheet 1 9- 28 POMR/ZAT/M 3/ 2/9/01?ART) 52.21%4P/17/N6 29 ,a f 27 swam/we Ell-WENT 24 25 POZAR/ZAT/ON 22SEPAPA TING car 5 .2 (PAZ/ PART) ,9 3

(PR/0P APT) H 51). (PR/OP ART} 26 Hg. 50. 45 (PP/0P ART) (PM A APT) 26BNWWM Agent April 6, 1965 AKIRA CHO ETAL NON-RECIPROCAL FERRITE SWITCHWITH ALTERNATE CONDUCTIVE AND RESISTIVE PLATES Filed 001.. 26. 1961 4Sheets-Sheet 2 I nvenlor:

April 6, 1965 AKIRA CHO ETAL 3,177,449

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVEPLATES 4 Sheets-Sheet 3 Filed Oct. 26. 1961 F/g M /05 02 /02 I10 I07 I061/! 105 Inventor; A. CHO T. KURODA Agent Apnl 6, 1965 AKIRA CHO ETAL3,177,449

NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVEPLATES Filed Oct. 26. 1961 4 Sheets-Sheet 4 Fig. /7.

I nven lor; A.CHOT. KURODA Agent United States Patent 3,177,449NON-RECIPROCAL FERRITE SWITCH WITH ALTERNATE CONDUCTIVE AND RESISTIVEPLATES Akira Cho and Takaji Kuroda, Tokyo, Japan, assignors to NipponElectric Company Limited, Tokyo, Japan, a corporation of Japan FiledOct. 26, 1961, Ser. No. 147,945 Claims priority, application Japan, Nov.15, B69, 35/ 45,707 Claims. (Cl. 333-11) This invention relates to amicrowave waveguide device and a microwave switching device employing aplurality of these microwave waveguide devices, and more particularly toa microwave waveguide device which can cause an electromagnetic wavethat enters into the waveguide along the axial line thereof in eithersense to pass therethrough without appreciable attenuation; and whichunder a predetermined condition can be in a matched state with respectto an electromagnetic wave which enters into the waveguide in one sensealong the axial line thereof and in a short-circuited state with respectto another electro magnetic wave that enters thereinto in the othersense. The invention intends to utilize this type of device in a novelmicrowave switching device so as to transmit only waves that areincident from particular one or plural input terminals to an outputterminal.

Microwaves have enjoyed an increasing popularity as a means forcommunication; now finding application in such diverse fields asmulti-channel telephony, television relay, data transmission teletype,etc. Where practical it has been customary to include in the overallsystem both an operational and a standby transmitter. The output sidesof the transmitters are connected to an antenna via a switching device;both transmitters being operated at all times. If the operationaltransmitter fails, the output of the standby is promptly switched overto the antenna so as to insure continuity of service.

Such a switching device must be capable of extremely rapid operationsince any interval results in interrupted service. Although theintelligence may not be significantly impaired in speech transmissioneven if the interruption lasts as long as one second, an unintelligiblecommunication may result in teletype or code transmission from this longa break in service especially where security gear is utilized insynchronization. Further in the case of numeric transmissionparticularly, the omission of only one numeral may result in a sequenceloss.

Such a switching device must also have a high decoupling ratio. Thedecoupling ratio of a switching device represents the extent to which itcan suppress the output of the spare transmitter when both the workingand the spare transmitters are in operation, and it is intended thatonly the output power of the working transmitter be supplied to theantenna through the switching device. If the decoupling ratio is poor, alarge amount of the output power of the spare transmitter will leak intothe antenna distorting communication. This distortion becomes serious asthe multiplicity of the channels increases.

The switching device must moreover be of a constant resistance type, orof the type wherein the impedance remains unchanged no matter whichtransmitter is feeding the antenna. In other words, the impedance of theswitching device must be matched .to the characteristic impedance ofeither transmitter whether or not that transmitter is being utilized atthe moment. If the matching is not perfect, the impedance as seen fromthe output terminals of either transmitter will vary according towhether or not that particular transmitter is feeding the antenna, withthe result that the modulation characteristics of the transmitters willvary. This will make it diffi cult to adjust the standby transmitter.Where a klystron is used as the transmitting tube the modulationcharacteristics deteriorate excessively with the result that adjustmentof the transmitter in standby becomes impossible.

In addition, it is preferable that such a switching device be small insize and simple in construction.

Of the various switching devices heretofore proposed, the most common ofthe constant resistance type, is that which comprises as a switchingelement the device described in Bell Telephone Patents Nos. 2,748,353and 2,887,664 wherein by means of a ferrite rod located in a magneticfield a Faraday rotation is induced in the electromagnetic wave. Such aswitching device requires, as will later be described in greater detail,two orthogonal polarization separating circuits with the result that thedecoupling ratio depends not only upon that of the switching element butalso upon each polarization separating circuit. Inasmuch as it isgenerally difficult to obtain a high decoupling ratio between twoorthogonal polarizations, the decoupling ratio of the polarizatinseparating circuit is usually less than that of the switching element.Therefore, the decoupling of a conventional constant resistance typeswitching device has been poor.

An object of this invention is to provide a novel microwave waveguidedevice which can cause an electromagnetic wave that enters thereinto,along the axial line of the waveguide in either sense, to passtherethrough without appreciable attenuation in one condition; and whichin a second condition is in a matched state with respect to an enteringelectromagnetic wave in one sense along the axial line of the waveguideand in a short-circuited state with respect to another enteringelectromagnetic wave in the other sense.

Another object of this invention is to provide a microwave switchingdevice which is of a constant resistance type, works rapidly, has thehighest possible decoupling ratio, and yet is small in size and simplein construction.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates schematically a conventional microwave switchingdevice;

FIG. 2 shows the input polarization separating circuit viewed in theaxial direction;

FIGS. 3a, 3b, and 3c show the switching element section of thewaveguide, viewed in the axial direction, with various degrees of fieldrotation;

FIGS. 4a and 4b show the output polarization separating circuit viewedin the axial direction with various degrees of field rotation;

FIGS. 5, 6 and 7 show an axial section, cross section, and brokenperspective views, respectively of an embodiment of the invention;

FIG. 8 shows the electric field direction in the waveguide;

FIG. 9 shows the waveguide device of the invention symbolically;

FIG. 10 shows the electric field in a circular waveguide;

FIG. 11 illustrates in perspective an insertion component with fourpairs of plates;

FIG. 12 is a perspective view of an embodiment of a microwave switchingdevice according to the invention;

FIG. 13 illustrates the device of FIG. 12 symbolically;

FIGS. 14 and 15 are top and side section views respectively of a portionof the device of FIG. 12;

FIG. 16 is a perspective view of a modified embodiment of FIG. 12 usingcircular waveguide, which nevertheless may still be shown symbolicallyby FIG. 13; and

FIGS. 17 and 18 illustrate symbolically two other examples of switchingdevices according to the invention.

Before entering upon a detailed description of the invention aconventional constant resistance microwave switching device, FIGS. 1-4,will be described in order to lay the groundwork for, and clarify theinvention.

The switching device of FIG. 1 is so composed that it may transmit theoutput of a working and a spare transmitter (not shown) connected toinput terminals 21 and 22, respectively, through input waveguides 23 and24 respectively to an input polarization separating circuit 25. In themiddle of a circular waveguide 26, at one end of which the polarizationseparating circuit 25 is formed, there is provided the conventionalswitching element 27 previously mentioned. At the other end of thecircular waveguide 26, where an output polarization separating circuit28 is formed, there are connected two output waveguides 29 and 30. Thewaveguide 29 has an output terminal 31 connected to an antenna (notshown) while the waveguide is terminated in a non-reflective load (dummyload) at 32. The input polarization separating circuit 25 is, as shownin FIG. 2, formed by attaching to the circular waveguide 26 the inputside waveguides 23 and 24 so that the axial lines thereof may beperpendicular to each other and to the axial line of the circularwaveguide itself. If the directions of the electric fields of theelectromagnetic waves in the input waveguides 23 and 24 are as shown byarrows 33 and 34, respectively, two electromagnetic waves travel in thecircular waveguide 26 along the axial line thereof, which are excited bythe first-mentioned electromagnetic waves, the electric fields of whichare shown by arrows 35 and 36, respectively.

If a magnetic field of predetermined intensity is impressed upon theswitching element 27 in the direction of the axial line of the circularwaveguide 26, the planes of polarization and hence the directions of theelectric fields of the electromagnetic waves travelling in the circularwaveguide 26 can be rotated in the desired sense by an amount of 90, sothat the directions of the electric fields of the two electromagneticwaves may be as shown in FIG. 3a by arrows 37 and 38. If the outputpolarizar tion separating circuit 28 is formed, as shown in FIG. 4a, byattaching to the circular waveguide 26 the output waveguides 29 and 30so that they may be parallel to the input side waveguides 23 and 24,respectively, one of the electromagnetic waves in the circular waveguide26, the direction of whose electric field is shown by an arrow 38 and isperpendicular to the axial line of the waveguide 29 which is connectedto the antenna, will excite the waveguide 29, while the other, thedirection of whose electric field is shown by arrow 37 and isperpendicular to the axial line of the waveguide 30 of thenon-reflection end, will excite the waveguide 30. Therefore, theelectromagnetic wave sent from the input terminal 21 is absorbed by thedummy load 32, and only the electromagnetic wave sent from the inputterminal 22 is transmitted through the output terminal 31 to theantenna. If the magnetic field is not applied to the switching element27, only the electromagnetic wave sent from the input terminal 21 istransmitted through the output terminal 31 to the antenna, while theelectromagnetic wave sent from the input terminal 22 is absorbed by thedummy load 32. Thus the switching device of FIG. 1 can selectivelytransmit to the antenna either one of the electromagnetic waves appliedto the input terminals 21 and 22, by applying or not to the switchingelement 27 a magnetic field in the direction of the axial line of thecircular waveguide 26. In order to supply the switching element 27 withsuch a magnetic field, it will be understood that an electric current ofthe desired sense and desired intensity is caused to ilow in a coil (notshown) wound about the circular waveguide 26 in the vicinity of theelement.

Inasmuch as the sense of the Faraday rotation, of the plane ofpolarization of the electromagnetic wave, caused by a ferrite, isreversed by the reversal of the sense of the magnetic field, switchingcan be made by the reversal of the polarity of the electric current inthe coil instead of making and breaking the coil current. Moreparticularly the directions of the electric fields in the circularwaveguide 26, of the electromagnetic waves which have passed theswitching element 27, can be rotated (if the coil current is in theproper sense and of the required intensity) from the directions shown inFIG. 2 (by the arrows 35 and 36) by 45 as shown in FIG. 3b by arrows 39and 40, respectively. And thus, if the output polarization separatingcircuit 28 is formed as shown in FIG. 4b, by attaching to the circularwaveguide 26 the output waveguides 29 and 30 so that the axial lines ofthese waveguides are perpendicular to the directions 39 and 40respectively and to the axial line of the circular waveguide 26, onlyone of the two electromagnetic Waves in the circular waveguide 26 (thedirection of the electric field of which is shown by the arrow 39) istransmitted through the waveguide 29 to the antenna. The other, movingin an electric field direction as shown by the arrow 40, that suppliedfrom the input terminal 22, is absorbed in the waveguide 30. If thesense of the electric current in the coil around the switching element27 is reversed, the two electromagnetic waves whose electric fields havethe directions shown in FIG. 2 by the arrows 35 and 36, after havingpassed through the switching element 27, will undergo electric fieldrotations of as shown in FIG. 30 by arrows 41 and 42. Here the reverseis true and now only that wave supplied from the input terminal 22 istransmitted through the waveguide 29 to the antenna.

In such a conventional switching device which may switch the rotationsof the planes of polarization between 0 and or between +45 and -45, thepolarization separating circuits 25 and 28 are indispensable. As hasbeen previously described the decoupling ratio of a polarizationseparating circuit is poor. This is because the electromagnetic wave inthe input side waveguide 23, for example, has in the neighborhood of thecircular waveguide 26 not only the component whose direction is shown bythe arrow 33 but also a component produced thereat in the directionperpendicular to the former direction, the ratio of these componentsgiving the decoupling ratio. Although the decoupling ratio can be madeconsiderably higher if the polarization separating circuit can be madecompletely symmetrical or if the method of excitation is carefullychosen, problems in manufacturing arise which are clilficult if notimpossible to solve. In the higher frequency range, it is especiallydifficult to make the decoupling ratio large since the dimensions of thewaveguide bccome correspondingly smaller.

Turning now to FIGS. 5 to 11 inclusive, an embodiment of the microwavewaveguide device according to the invention will now be described.

As shown in FIGS. 5-7 rectangular waveguide 51 has contained therein acylindrical ferrite rod 52, both ends of which are tapered to asharp-point. The waveguide 51 has broad and narrow pairs of walls whichare also known as the a and b walls, respectively. Contiguous to the rodon either side are two substantially rectangular metal plates 56 and 57,the dimensions of which are such that the rod lays in a coaxial positionwith respect to the axial line 53 of the waveguide 51. The metal platesfit snugly between the outer cylindrical surface of the ferrite rod andthe inner surfaces of the waveguide 51 that include the narrow walls.The two substantially rectangular resistance plates 58 and 59 aresimilarly positioned at the other end of the rod, and may consist of anydielectric enameled with resistive film. In addition, the metal plates56 and 57 and the resistance plates 58 and 59 are all in a plane whichcontains the axial line 53 and which is perpendicular to the b walls ofthe waveguide 51. Edges 68 and 69 of the metal plates 56 and 57, whichare perpendicular to the edges contiguous the rod and waveguide areadjacent the end 70 of the cylindrical portion of the ferrite rod 52.Edges 73 and 74 of the resistance plates 58 and 59 which areperpendicular to the edges contiguous the rod and waveguide aresimilarly positioned with respect to the other end 75.

In order to support the piece parts 52, 56, 57, 58, and 59, hereinafterreferred to as the insertion component, in the manner explained above ithas been found advantageous to introduce the insertion component (intothe waveguide) between a pair of supporting pieces 81 and 82 which aremade of foamed polyethylene or the like. These supporting pieces aremirror images of each other and have such shape and dimensions that whenput in a juxtaposed relation, they fill the air gap in the section ofthe waveguide containing the insertion component. The lengths of thesupporting pieces 81 and 82 in the direction of the axial line 53 of thewaveguide 51 may be chosen so as only to meet the requirements forsupport. Although foamed polyethylene is preferable, because thedielectric constant thereof is nearly equal to that of the air andtherefore it does not disturb the electrical characteristics of thewaveguide 51, the supporting pieces 81 and 82 may be made of otherequivalent materials. Also, because of the proximity of the dielectricconstant of polyethylene to that of air it is not requisite that thesupporting pieces form-fit the insertion component and in fact they maybe eliminated and replaced by any suitable means for supporting theinsertion component.

Coil 83 is wound around the waveguide so as to pro duce a uniformmagnetic field in the direction of the axial line 53 at least at theportion of the insertion component 80. Waveguide 51 is further providedwith two flanges 84 and 85 at both ends thereof to facilitateconnections with other waveguides (not shown).

The electromagnetic wave which travels along the axial line of such arectangular waveguide 51 is generally of H mode, and the direction ofthe electric field is, as shown in FIG. 8 by arrows 86, parallel to theabovementioned 1: walls and perpendicular to both the metal andresistance plates.

Such a waveguide device is shown diagrammatically by the symbol in FIG.9, wherein an arrow 87 is in the direction from the flange 85 to theflange 84, or from the resistance plates 58 and 59 to the metal plates56 and 57 of FIGS. -7.

When a magnetic field in the direction of the axial line of thewaveguide device is produced by causing an electric current flow throughthe coil 83 thereof, the impedance of the device as seen in a firstsense from the resistance plates to the metal plates (from the flange 85to the flange 84) the sense shown by the arrow 87 of FIG. 9, is matchedto the characteristic impedance of the waveguide and accordingly thedevice does not reflect the electromagnetic wave travelling in thissense, whatever direction the current may be flowing in coil 83. Theimpedance of the device as seen in a second sense opposite to the first,is a short-circuit and thus theoretically produces full reflection. Whenno electric current is caused to flow through the coil 83 and there isno magnetic field in the direction of the axial line 53, the waveguidedevice shows substantially the same characteristics as the waveguideitself, without the insertion component, with the result that anelectromagnetic wave can pass through the waveguide device in eithersense without substantial variation.

The theoretical reasoning behind the invention is presumably as follows.When no electric current flows through the coil 83, an electromagneticwave having an electric field perpendicular to the metal plates 56 and57 and the resistance plates 58 and 59 is not electrically affected bythese plates and passes therethrough without any appreciable attenuationand reflection, but with only a slight loss caused by the ferrite rod52. However, when an electric current flows through the coil 83, thedirection of the electric field of the electromagnetic Wave which passesthrough the waveguide device is rotated in a sense determined by thesense of the electric current in the coil 83 on account of the Faradayrotation induced by the magnetic field at the ferrite rod 52. Which everthe sense of the rotation may be, the electric field takes on acomponent parallel to the surfaces of the plates and the electromagneticwave is attenuated at the resistance plates and is reflected at themetal plates. Thus an electromagnetic wave which travels in thewaveguide device in the first sense or from the resistance plates to themetal plates is absorbed at the resistance plates, while that whichtravels in the second sense is reflected by the metal plates. Due to theFaraday rotation of the electric field, the electromagnetic wave willtake on an excess amount of this field component having a directionperpendicular to the b walls and the cutoff frequency of the waveguide51 will approach the frequency of the electromagnetic wave. Therefore,the rotation is suppressed on one hand, and is forcibly caused onaccount of the Faraday rotation on the other hand, with the result thatthe electric field of the electromagnetic wave is in a forcibly rotatedstate. Thus it is possible to cause remarkable attenuation in anelectromagnetic wave travelling in the waveguide in the first sense, ifthe shape, diameter, and length of the ferrite rod 52, the dimensions ofthe metal plates 56 and 57, the dimensions and the resistances of theresistance plates 58 and 59, and the relative positions of such pieceparts are empirically varied for best results.

In an experimental example, the frequency of the elec tromagnetic wavewhich is caused to pass through the waveguide device was 7,000 me; thewaveguide 51 was 15.8 mm. x 34.8 mm. in cross-section; the ferrite rod52 was 7.5 mm. in diameter and about 60 mm. long; the number of turns ofthe coil 83 was 2,500 turns per 70 mm.; the exciting current was 450 ma;the metal plates 55 and 57 were about 23 mm. x 13 mm., respectively; andthe resistance plates 58 and 59 were about 9.5 mm. x 13 mm. and hadohms/cm. respectively. The obtained attenuation was 40 db, and variedwithin the range 3550 db in accordance with variations in the ambienttemperature and the exciting current.

In the embodiment previously described, a rectangular waveguide was usedand the plates extended from the surface of the ferrite rod 52 to theinner surfaces of the guide. The rectangular waveguide may, however, bereplaced by a circular waveguide or other waveguide which has any shapeof cross-section; the metal plates 56 and 57 and the resistance plates58 and 59 do not have to extend from the surface of the ferrite rod 52to the inner surfaces of the rectangular waveguide or the inner surfacesof the waveguide of other form but may be placed, as the case may be,only between the surface of the ferrite rod and one of the innersurfaces of the waveguide. Also, the positions of the metal and theresistance plates relative to the ends of the ferrite rod 52 do notnecessarily have to be as mentioned above but it is sufficient that theyare positioned nearer to one end and the other end of the waveguide,respectively. The ferrite rod 52 may also deviate a little from theaxial line 53 since this is not critical, but not too much since theattenuation will be affected. If the insertion component is so supportedthat the metal and the resistance plates are perpendicular to the bwalls,

the waveguide device is as previously mentioned, in a earns r9 matchedstate with respect to an electromagnetic wave travelling therethrough inthe first sense and in a shortcircuited state with respect to anotherelectromagnetic wave travelling in the second sense when there is amagnetic field. When no electric current flows in the coil 83, anelectromagnetic wave travelling in either direction passes throughwithout substantial attenuation. If the insertion component is supportedin a rectangular, circular, or other waveguide at a certain radialposition, the waveguide device will give similar results depending uponthe positioning of components with respect to the field. In this regard,it is to be noted that if the circular waveguide 88 shown in FIG. 10 isexcited so as to propagate only the dominant mode H the direction of theelectric field of the electromagnetic wave being determined by the modeof the excitation (e.g. shown by an arrow 89) the best result isobtainable when the circular waveguide is so excited that the directionshown by the arrow 89 is perpendicular to the plane of the metal andresistance plates of the insertion component. In contrast to therectangular waveguide in which the Faraday rotation of the plane ofpolarization of the electromagnetic wave is a very particularphenomenon, the plane of polarization in a microwave waveguide device ofthe invention wherein a circular M waveguide is used is freely rotatedin accordance with the intensity of the magnetic field.

The insertion component may, as shown in FIG. 11, be modified so thatthe ferrite rod 52 is included between two pairs of metal plates 90, 91,92, 93 (which are similar to the metal plates 56 and 57 shown in FIGS.57) and two pairs of resistance plates 94, 95, 96 and 97 (which aresimilar to the resistance plates 58 and 59 of FIGS. 5-7) similarly tothe manner explained in connection with FIGS. 5 to 7 except that herethe metal and resistance plates contact one another. If this modifiedinsertion component is similarly supported in a rectangular waveguideand an electric current of required intensity is caused to flow in thecoil 83, then the electromagnetic wave which travels through thewaveguide device in the first sense undergoes considerable attenuationat the first set of resistance plates 96 and 97 and is reflected at thesucceeding metal plates 92 and 93 to again undergo attenuation at thefirst resistance plates. In the same manner that part of theelectromagnetic wave which leaks through is affected by the next set ofresistance plates and metal plates eventually being totally absorbed,with the result that the impedance of the waveguide device seen in thefirst sense or from the flange 85 is in a matched state. In a likemanner the waveguide device is in a short-circuited state with respectto the electromagnetic wave which enters in the second sense. It is tobe noted. however, that the mere increasing of the number of pairs ofmetal and resistance plates does not necessarily result in greaterattenuation and more perfect short-circuiting, but that such a waveguidedevice shows the best effects when the dimensions of these plates, theintensity of the electric current in the coil 83 and so forth areempirically varied for best results. It is not imperative that theplates be touching and gaps may be included between the metal and theresistance plates in the axial direction of the ferrite rod 52.

In the embodiment and modifications described above. the ferrite rod 52was cylindrical and sharp-pointed at both ends. The ferrite rod, mayhowever, instead of being cylindrical have the cross-section of anypolygon. Electrically, both ends are preferably sharp-pointed, but thisalso is not a necessary condition though it gives better results. Thegreater length and the diameter of the ferrite rod 52 are, the less thestrength of the magnetic field to be applied in direction of the axialline 53 by the coil 83 need be; but this variation is accompanied by anincrease in the loss caused by the insertion com ponent. The diameterand the length of the ferrite rod are decided, therefore, by acompromise between the loss caused by the insertion component and themagnetic field to be applied.

The frequency range of the electromagnetic wave controllable with themicrowave waveguide device of the invention depends on the maximumfrequency of the electromagnetic wave at which the ferrite rod does notgive appreciable loss and can effect the Faraday rotation. In any eventthe waveguide device can sufficiently achieve its purpose within theband of 1,000 Inc-5,000 mc., which is used in the present-daytelecommunication.

Turning now to FIGS. 12 through 18 inclusive, a microwave switchingdevice according to the invention will be described. It is to be notedhere that, unless otherwise stated, the metal and resistance plates, ofthe microwave waveguide device, in the embodiments to be described areperpendicular to the electric field of the electromagnetic wave in theabsence of a magnetic field.

The microwave switching device of the invention, which is perspectivelyshown in FIG. 12 and schematically shown in FIG. 13 by using the symbolof FIG. 9, is composed of a branch waveguide 101, which is preferably anE-branch waveguide, and the microwave waveguide devices 50 and 51'(similar to FIGS. 5-7) of the invention which are connected to thebranch waveguide in such a manner that the metal plates of the insertioncomponent of the waveguide devices are disposed inwardly; the flanges 84and 84' are connected to flanges 102 and 103 of the E-branch waveguide101. The flanges and 85 which are positioned at both ends of theswitching device of FIG. 12 serve as input terminals, while a flange 105which is positioned at the end of an E-arm 104 serves as the outputterminal.

As shown in FIGS. 14 and 15, which are a top view and a longitudinalsectional view of the portion including the E-branch waveguide 101, ametal plate 106 is placed in the E-arm 104 perpendicularly to the axialline thereof so as to leave a window 107 adjacent the metal plate 106,in order to provide the E-arm with susceptance. Another metal plate 113having a member 112 is experimentally inserted into arm 110 in such amanner that the metal plate 113 may short-circuit the arm. The positionof the metal plate 113 is adjustable in the direction of the axial lineof the main arms 110-111 by means of the handle 112, so that theimpedance of the main arms 110-111 as seen from the arm 111 to the arm110 may be adjusted to the characteristic impedance of the main arms.The reason for this will be obvious later.

As has been described, the impedance of the microwave waveguide deviceas seen from its flange 84 which is the one nearer to the metal plates56 and 57 is in the short-circuited state when the coil 83 is excited.It follows therefore that it the length of the arm 110 is so chosen suchthat the position at which the microwave waveguide device isshort-circuited will coincide with the position of the metal plate 113at which the metal plate would match the impedance of the E-branchwaveguide 101 and if the waveguide device 50 and the E-branch waveguide101 are connected with each other, the impedance as seen from the arm111 will be in a matched state when the coil 83 is excited. Assuming theabsence of device 50 for the moment this leads to the result that,inasmuch as the microwave device 50 serves as a nonreflectivetermination with respect to an electromagnetic wave that has enteredinto the device from the flange 103 and has passed through the branchpoint and is entering the arm 110, the electromagnetic wave from theflange 103 is completely sent to the flange 105 of the E-arm 104.Inasmuch as the microwave waveguide device 50 will also serve as a dummyload directly for another electromagnetic wave that has entered into thedevice from the flange 85, the electromagnetic Wave initiating fromthere undergoes large attenuation and does not reach the flange 105.Although the object of the invention is partly attainable even if theposition at which the microwave waveguide device 50 is short-circuitedis not made to coincide with 9 the above-mentioned impedance-matchingposition of the metal plate 113, the best results will not be obtainedsince the impedance of the device seen from the flange 103 is notmatched with the characteristic impedance of the device in the excitedstate of the coil 83 and so some of the electromagnetic wave isreflected.

Now with another microwave waveguide device 50 similarly connected tothe E-branch waveguide 101 (in the above-mentioned manner) it will beappreciated that if the coil 83 is excited and the coil 83' is not, anelectromagnetic wave from the flange 85 does not appear at the flange105; only the electromagnetic wave from the flange 85 appearing therewithout any appreciable loss. If on the other hand coil 83 is notexcited and only the coil 83 is, only the electromagnetic wave from theflange 85 is sent to the flange 105. In this manner the microwaveswitching device of FIG. 12 of the invention can selectively transmitone or the other of the output powers of two transmitters connected tothe flanges 85 and 85 which serve as the input terminals, respectively,to the flange 105 which serves as the output terminal.

The embodiment of the microwave switching device depicted above is ofthe constant resistance type, because the impedance of the device asseen from the input terminal 85 is always in match with thecharacteristic impedance of the microwave waveguide device 50 eventhough either or both of the coils 83 and 83' may be excited and becausethe impedance seen from the input termnial 85 also is similarlyconstant. The time required for switching is short, since the switchingoperation is performed by interchanging the excitation of the coils 83and 83' to produce in either of the microwave waveguide devices 50 or50' an axial magnetic field.

The coils 83 and 83' may be wound directly around the waveguides withoutloss of effectiveness, which fact makes it possible to reduce the wholedimensions of the microwave switching device and lessen the number ofturns of the coils; with the result that the time required for switchingis further shortened. Furthermore, the decoupling ratio between theinput terminals 85 and 85' can be made sufficiently large, because thedecoupling ratio of a polarization separating circuit which has beenindispensable to the conventional switching device can be eliminated andbecause it is possible to design the microwave waveguide devices 50 and50 in such a manner that each of them may effect a very largeattenuation to the electromagnetic wave entering thereinto from theflange 85 or 85' when the coil 83 or 83' is excited. If the microwaveswitching device according to the in vention is composed of rectangularwaveguides, which are at least three in number and which lead to theworking and spare transmitters and to the antennna, not only can theswitching device he reduced in size and weight, but also the wholetransmitting equipment can be reduced in size and weight since it isusual to employ rectangular waveguides at the output ends of bothtransmitters and at the input terminal of the antenna.

As has been previously described, the microwave waveguide device of theinvention may be composed of a circular waveguide in place of therectangular waveguide 51 shown in FIGS. -7. Referring to FIG. 16, whichis a perspective view of another embodiment of a microwave switchingdevice according to the invention it may be seen that mircowavewaveguide devices 50a and 50a are composed of circular waveguides. It isto be noted that instead of the flange portions 84, 102, 84' and 103 (asin FIG. 12) integral waveguides are used; otherwise similar functioningpart are designated with like numerals. Inasmuch as the most preferableresult is 0btained when the microwave waveguide devices 50 and 50 areexcited in such a manner that the directions of the electric fields ofthe electromagnetic waves at the input terminals 85 and 85' areperpendicular to the metal and resistance plates, rectangular waveguides120 and 120 are connected to the ends of the circular waveguides so asto facilitate such excitation. This switching device performs theswitching operation in a like manner to that of FIG. 12.

In the microwave switching devices so far described the direction of themagnetic fields produced by the coils 83 and 83' are substantially thesame. Therefore, the magnetic field produced by one of the coils will,under some circumstances, affect the microwave waveguide device to whichthe other of the coils belongs. FIG. 17 shows another microwaveswitching device where this condition may be relieved. Here themicrowave waveguide clcvices 50 and 50 of the invention are so connectedto the branch waveguide 101 that their axial lines are perpendicular toeach other, thus eliminating any field interference.

Referring to FIG. 18 which is a symbolic system diagram of still anotherembodiment of the microwave switching device of the invention, theswitching device 130 is so designed as to selectively transmit only oneof the input powers supplied to more than three input terminals to theoutput terminal 105. In this switching device the microwave waveguidedevices 50, 50', 50", and 50' which have input terminals 85, 8S", and85, respectively, and which are equal in number to the input power to beswitched are connected to a branch waveguide 131 in such a manner thatno two axial lines of the waveguide devices are aligned and that theabovementioned condition is satisfied. Coils 83, 83', 83", and 83" ofthe Waveguide devices are so arranged (not shown) that it is possible torefrain from exciting any selected one of the coils into which the inputpower to be transmitted to the output terminal enters, and to excite allof the remaining coils. Such an arrangement is simply conceived and asit is well known it will not be gone into. It is to be understood thatsuch a morethan-three-input switching device may also be obtained byproviding the arm having the output terminal 105 of the switching devicedescribed with reference to FIGS. 12 through 17 inclusive, with anothermicrowave waveguide device of the invention, thus pyramiding thedevices.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention, as set forth in the objects thereof andin the accompanying claims.

What is claimed is:

1. A non-reciprocal waveguide device comprising: a waveguide, a ferriterod disposed substantially coaxially in said guide, at least one pair ofplates, each pair consisting of a conductive plate and a resistiveplate, disposed successively along the axis of said rod between thesurface of the rod and the inner surface of the guide such that aresistive plate is closer to one end of said rod and a conductive plateis closer to the other end of said rod, means for supporting said rodand plates, and means for applying an axial magnetic field to said rod.

2. A non-reciprocal waveguide device as set forth in claim 1 in which aneven number of pairs of plates are provided and positioned in a planepassing through the rod axis and wherein said plates are positionedsymmetrically in said plane on opposite sides of said rod such thatsymmetrically related plates have the same wave transmissioncharacteristics.

3. A non-reciprocal waveguide device as set forth in claim 2 in whichthe waveguide has a rectangular crosssection and the plates arerectangular vanes and wherein said plane passing through the rod axis isperpendicular to the narrow walls of said guide.

4. A non-reciprocal waveguide device as set forth in claim 1 in whichsaid rod has tapered ends and wherein the plates lie successively alongthe axis of said rod with in planes defined by the end portions of saidrod less said tapered ends.

5. A non-reciprocal waveguide switching device comprising a branchwaveguide having at least two input waveguide portions and an outputwaveguide portion; a non-reciprocal waveguide device as set forth inclaim 1 positioned in each input waveguide section such that theconductive metal plate is disposed on the side nearest the branchwaveguide junction and wherein the output waveguide portion is of finitelength and is connected on a one to one ratio to each input portion,each nonreciprocal waveguide device being electrically displaced fromthe branch waveguide junction such that the characteristic impedance isseen when looking from an unenergized non-reciprocal device toward thejunction when another non-reciprocal device is energized.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCESGoodwin, Proceedings of the IRE," January 1960, page 113.

Tomkins et al.: Journal of Applied Physics," Supplement to vol. 31, No.5, May 1960, pages 1765-1775.

1. A NON-RECIPROCAL WAVEGUIDE DEVICE COMPRISING: A WAVEGUIDE, A FERRITEROD DISPOSED SUBSTANTIALLY COAXIALLY IN SAID GUIDE, AT LEAST ONE PAIR OFPLATES, EACH PAIR CONSISTING OF A CONDUCTIVE PLATE AND A RESISTIVEPLATE, DISPOSED SUCCESSIVELY ALONG THE AXIS OF SAID ROD BETWEEN THESURFACE OF THE ROD AND THE INNER SURFACE OF THE GUIDE SUCH THAT ARESISTIVE PLATE IS CLOSER TO ONE END OF SAID ROD AND A CONDUCTIVE PATEIS CLOSER TO THE OTHER END OF SAID ROD, MEANS FOR SUPPORTING SAID RODAND PLATES, AND MEANS FOR APPLYING AN AXIAL MAGNETIC FIELD TO SAID ROD.